Diaphragm Dysfunction and Respiratory Complications in the Perioperative Setting- Can Diaphragm Ultrasound Aid Prediction?

Background

A considerable part of the population undergo surgery every year and in Sweden around 600,000 surgeries are registered yearly. Occurring complications after surgery include wound infections, urinary tract infections, venous thromboembolism and pneumonia. Postoperative pneumonia is the third most common complication and increases morbidity and mortality substantially(1). Furthermore, it prolongs hospital length of stay (LOS), increases medical costs and hospital readmissions. The incidence of postoperative pneumonia is dependent on non-modifiable factors such as type of surgery, age, sex and preoperative functional status but also on modifiable factors like smoking and adherence to preventive bundles(2). However, pneumonia preventive bundles are more studied and used in the ICU than in the perioperative setting. The current burden of postoperative pneumonia in Sweden is presently unknown. Furthermore, few prognostic examinations and preventive measures are used in the perioperative setting. It is well known that diaphragm dysfunction affects patients after major abdominal surgery and that it affects outcome postoperatively(3, 4). The mechanism behind the diaphragm dysfunction is unclear but animal studies indicate that postoperative inflammation may weaken the diaphragm only hours after exposure(5). Postoperative respiratory complications are partly due to a deteriorated diaphragm function and cause increased morbidity and mortality(6). In cardiac and upper abdominal surgery patients, ultrasound measurements of diaphragm excursion and thickening proved useful in ruling out diaphragm dysfunction(7, 8).

Diaphragm dysfunction can be diagnosed using ultrasound measuring diaphragm excursion, diaphragm thickness, thickening or diaphragm density. The examinations have high intra- and inter-observer reliability, are non-invasive and non-ionizing imaging techniques. This is in sharp contrast to twitch magnetic phrenic nerve stimulation, the golden standard technique for measuring diaphragm function, being reliable but invasive(9). Electric impedance tomography (EIT) is a non-invasive radiation-free imaging technique that provides real-time images and data of regional lung ventilation and lung volumes (10) and the correlation to diaphragm dysfunction and the later development of atelectases as assessed with ultrasound of the diaphragm is not clear. Furthermore, parameters on lung volumes retrieve with spirometry also lack a clear relationship with diaphragm ultrasound parameters and later respiratory complications.

Diaphragm ultrasound has previously been used to identify severe dysfunction. However, to identify early signs of dysfunction could render important actions perioperatively to avoid progression and continuation of early diaphragm dysfunction and hence an increased risk of complications.

Gap of knowledge Can diaphragm ultrasound in the peroperative setting predict respiratory complication after dismissal from postoperative ward? And can diaphragm dysfunction as defined with ultrasound be correlated to changes in lung volumes and lung function as demonstrated with EIT and spirometry?